1. Field of the Invention
The present invention relates to an electrostatic chuck device.
2. Description of the Related Art
In general apparatuses for manufacturing semicon ductor devices, a vacuum chuck is employed as a means for holding a object to be processed, for example a semiconductor wafer.
In a vacuum treatment apparatuses such as an ion injection apparatus or a plasma etching apparatus, it is necessary to hold and treat a semiconductor wafer in a vacuum atmosphere. Thus, it is not possible to use the vacuum chuck as adsorption/holding means.
Means for electrostatic chucking semiconductor wafers in a vacuum are disclosed, for example, in Published Unexamined Japanese Patent Application (PUJPA) No. 59-79545, PUJPA No. 60-197335, PUJPA No. 62-29140, PUJPA No. 63-95644, Published Examined Japanese Patent Application (PEJPA) No. 1-36707, and PEJPA No. 1-52899.
According to one of the above apparatuses, first and second adsorbing sections are provided on the adsorption surface of a holding base, and a DC voltage is applied between the electrodes of the first and second adsorbing sections. In this apparatus, dielectric polarization is caused to occur in a dielectric layer interposed between the semiconductor wafer and electrodes. By virture of the van der Waals force due to the dielectric polarization, the semiconductor wafer is attracted and held. According to another of the above apparatuses, a single-phase alternating current is applied for an electrostatic chuck device between an electrode and a semiconductor wafer, or between electrodes of first and second electrostatic chucking sections.
According to an apparatus wherein a DC voltage is applied between a wafer and an electrode or between two electrodes, an attraction force (Coulomb force) is strong, but dielectric polarization occurs in dielectric material at the surface. THus, even after the application of voltage is stopped, the charge remains on the electrostatic chucked face and the chucked object is not easily separated from the chucking/holding base. Besides, dust or the like is easily attached to the semiconductor wafer which is the held object.
On the other hand, if an AC voltage, in lieu of the DC voltage, is applied, the amount of dust attached to the chucked object can be reduced. In addition, since no dielectric polarization occurs in dielectric material, the chucked object is immediately separated from the chucking/holding base upon the turning-off of voltage application between electrostatic chucks. In the prior art disclosed in the above prior art documents, however, what is applied is the single-phase AC voltage; therefore, sufficient attraction force cannot be obtained. Because the single-phase AC voltage takes a zero value instantaneously at every regular cycle, and the chucking force is lost at the instantaneous zero voltage time.